1. Field of the Invention
An apparatus consistent with the present invention relates to a device for controlling the projection lens shift of a projector.
2. Description of the Related Art
With the development of information technologies, a video projecting apparatus using a liquid crystal display (LCD) has been widely supplied and developed to meet the need to reproduce images on a large screen.
The video projecting apparatus generally comprises a projector for producing, enlarging and projecting images on a screen. The projector can be classified into two types, such as a front projection type and a rear projection type, depending on how images are projected on the screen.
The front projection type projector comprises a light source for generating light, an image generator for generating images and a projection lens module with a plurality of projection lenses for enlarging and projecting generated images on the screen.
The image generator consists of a means for splitting light emitted from the light source, for example, into three colors of red, green and blue, a liquid crystal panel for receiving and outputting split light and a prism. The image generator and the projection lens module are inclusively called “an engine part” which is mounted within a case.
The project lens module comprises first and second projection lens units which approach and separate from each other in order to focus an image projected on the screen.
A lens shift control device is provided to adjust the height of the projection lens module by moving the module upward or downward. FIG. 1 illustrates a lens shift control device as disclosed in Korean Patent Publication No. 10-1998-063831. Referring to FIG. 1, a projection lens module 1 comprises a plurality of lens barrels 2, 3 and 4 and is supported by a support plate 5 which can vertically slide along a rail 6a of a frame 6. When a shift rod 8 connected on a retainer 7 fixed to the frame 6 is rotated, a bolt section 8a of the shift rod 8 interacts as a screw with a nut section 9 fixed to the support plate 5. Accordingly, the frame 6 moves up and down, thereby enabling the user to adjust the height of the projection lens module 1.
In the conventional lens shift control device, since one end of the projection lens module 1 is supported by the support plate 5, the other end is apt to slope down due to the weight of the projection lens module 1. Therefore, the friction between the rail 6a and the support plate 5 increases, and the projection lens module 1 is prevented from smoothly shifting up and down. As a result, a great force is required to shift up the projection lens module 1 which is sloped due to its own weight.
In addition, since the shift rod 8 is displaced from the center of gravity of the projection lens module 1, the user needs to apply much force to operate the shift rod 8.